1. Field of the Invention
The subject of the present invention is a device for monitoring an enclosure, in particular the hold of an aircraft.
2. Description of Related Art
The hold of an aircraft contains containers or objects which are moored to the floor, so as to be immobilized during the movement, in particular the flight, of the aircraft. It is advisable to ensure that, in the course of the movement of the aircraft, there is no movement of the containers or other objects inside the hold, such movement possibly resulting in damage to the structure of the aircraft with damaging consequences.
It is also important to be able to continuously monitor the hold of an aircraft so that the crew can immediately be warned in the event of the appearance of smoke, a fire, or a hot spot resulting, for example, from an electrical short circuit.
Hitherto, these various requirements have been fulfilled to a greater or lesser degree with the aid of various types of sensor. There are optical sensors or ion sensors, which essentially detect smoke by measuring any opacity between an emitter and a receiver. The number of sensors required to fit out a hold in this way is very, but this does not deliver a perfect result, insofar as the smoke detections are performed belatedly and these detectors are sensitive to the environment (pressure, humidity, dust), giving rise to false alarms, which nevertheless require that the aircraft return to the airport. It is also known practice to use video cameras of CCD type, which operate in the near infrared and are associated with an image-processing computer, with a monitor in the cockpit of the aircraft, for displaying the hold of the craft.
The drawbacks of the known systems are:
the point-like nature of the detections of fires, smoke and hot spots, giving no details regarding the volume coverage, the shape factor of the fire or of the smoke, the geographical density of the smoke or the displaying of the distribution of the hot spots;
the various detection systems are separate, requiring as many computers as types of detection as well as a large number of sensors, since the latter are all specific to one type of detection;
the known systems give no details regarding the movement of the loads contained in the hold and regarding any impairment to the aircraft resulting from the shifting of such loads.
It would be possible to make temperature measurements with the aid of infrared thermographic cameras. Such cameras are very big, their spatial resolution is low, and their cost very high. This solution is therefore not implemented.
Monitoring cameras with an infrared projector and elements which are sensitive to this type of radiation are already known, for example from documents DE 19542481C1 and DE 3812560A1, or else U.S. Pat. No. 5,085,525, but these are essentially fixed cameras envisaged for use outdoors and not designed for the monitoring of a closed enclosure, and in particular an aircraft hold subjected to vibrations, accelerations, temperatures and other more or less severe conditions. Moreover, these documents limit themselves to the description of cameras, constituting sensors, without truly describing a complete system together with processing of the signals delivered by these sensors.
The object of the invention is to provide a device for monitoring an in particular, in particular the hold of an aircraft, which makes it possible with the aid of a single type of sensor of simple design and of a single type of computer, to accomplish several functions for detecting fires, smoke, hot spots, movements of load, and for visualization of the enclosure, in particular the hold of an aircraft.
To this end, the monitoring device to which it relates comprises at least one sensor consisting of a CCD camera of very short spectral band lying between 0.4 xcexcm and 1.1 xcexcm, fitted with an infrared filter eliminating the spectral band lying between around 0.4 xcexcm and 0.8 xcexcm, this sensor being associated with a computer catering in particular for image processing, by means of a display screen and a control board.
This type of video camera can detect hot spots, for temperatures lying between around 350 and 600xc2x0 C., corresponding to the spectral band lying between 0.8 and 1.1 xcexcm.
Advantageously, each camera is associated with a near infrared lighting element, each lighting element consisting, for example, of an 880 nm silicon element.
According to another characteristic of the invention, each camera and the associated lighting element are housed inside a sealed box closed by a porthole. It is interesting to note that, in the spectral band of the CCD camera, the spectral transmission factor of the porthole is a constant which depends only on the thickness of the material traversed. Insofar as each camera is associated with one lighting element, the camera makes it possible to perform other types of detection, especially detections of fires, smoke or movements of load, and to display the enclosure within which this camera is placed. This device is advantageous in the sense that all the sensors are of the same kind and are associated with one and the same computer and with one and the same control board.
According to another characteristic of the invention, the box also contains a temperature-regulating device and/or a device for de-icing the porthole, as well as a supply, command and control block.
The device can thus operate in various environments, especially under variable humidity, pressure and temperature conditions, without these conditions affecting its reliability.
As far as the lighting is concerned, it is not continuous, since the computer brings about the lighting of each lighting element for durations, for example, of between around 40 and 100 milliseconds. It is thus possible to procure results delivered by each camera, without lighting, for example for thermographic measurements or certain measurements of fire, and the measurements requiring lighting, such as the measurements of the presence of smoke, of movements of the load, or of displaying of the inside of the hold. The images may be acquired with greater or lesser integration times.
According to one characteristic, this device compares two images, one of which constitutes a reference image, which are acquired successively so as to detect variations in the position of the objects lying in the field of each camera. It is thus possible to detect the movement of a load, based on a comparison of images. In the case of an aircraft hold, the image of the load forming the reference is stored before the craft takes off, a real-time comparison of the image of the hold relative to the reference image during the flight, making it possible to detect geographical variations of the load and to pinpoint and measure these variations. The system allows a resolution determining a shifting of the load relative to the hold of a value of 50 mm to 15 m with a horizontal angle of 30xc2x0.
The device also allows the pinpointing, in three dimensions, of an object of the scene, using  less than  less than monocular greater than  greater than  vision, provided that the object is furnished with a locating pattern. It also makes it possible, by this means, to dynamically track the object within the scene. To this end, an autocalibration of detection on a plane locating pattern is carried out, this locating pattern being known by the system. The following parameters are extracted from the calibration: geometrical distortion, focal length, style of pixel discretization, optical centre. Automatic extraction of the points of the locating pattern is carried out, together with correction of the distortion on the basis of the parameters and matching of the distorted points with the object model, and finally pinpointing (translation, rotation, hence distance from the object to the camera) on the basis of the previous steps.
Regardless of the process used to pinpoint the objects and to detect their movements, the device is rendered insensitive to interfering phenomena of the vibration type.
Furthermore, this device analyses the histogram of the grey levels of an image provided by a camera with counting of the points having a level higher than a predetermined threshold and forming a connected region of the image, so as to deduce therefrom the existence and the extent of a zone of fire. A detection is triggered upon variation of the histogram of the image, from which is deduced, on the one hand, the extent of the zone of fire by counting the minimum number of continuous pixels of the image and, on the other hand, the level of the points of the zone of fire, that is to say the minimum threshold on the various pixels, by performing a discrimination of the interfering phenomena, such as those resulting from the sun or from an incandescent lamp.
Furthermore, this device analyses the distribution of the grey levels as well as the number of classes present in each image delivered by a camera so as to detect the possible presence of smoke.
The detection of smoke is based on pinpointing in the image a rise in luminosity related to the opacity of the smoke, given that this image is delivered while the lighting element is operating. Detection is triggered by variation of the histogram of the image, from which one deduces the mean degree of opacity which gives rise to a percentage heightening of the image, due to the diffusion of light and the extent of the smoke zone. The fog/smoke discrimination is carried out with the aid of a hygrometric sensor situated in the enclosure, or by analysing the spatio-temporal gradient of diffusion, given that the gradient of the change in transmission of smoke is small, whereas the transmission gradient in fog is large.
The computer is linked to at least one alarm to which a signal is delivered upon detection of an anomaly. When monitoring the hold of an aircraft, the crew of the latter can, in the event of detection actioning an alarm, and by virtue of the screen, use the device as a display device allowing a view of the inside of the hold, so as to check whether this detection is justified and does not result from an operating fault.